The present invention relates to a method for producing an aromatic primary amine in a high yield in which an aromatic nitrile is hydrogenated under a low pressure condition.
Aromatic amine is a useful compound as an industrial raw material, and is utilized in a variety of field such as those of medicine, agricultural chemical, dye, surfactant and chemical agent. Many proposals have been made as for methods for producing primary amine by hydrogenation of aliphatic nitrile. On the contrary, it is well known in the art that production of primary amine through hydrogenating aromatic nitrile is much more difficult than starting from aliphatic nitrile, since hydrogenation of the aromatic ring may proceed, or a large amount of secondary amine may be by-produced. In fact, only four methods described below have ever been proposed, in which aromatic nitrites employed are limited to those having no substituent on the aromatic ring, such as benzonitrile, 3-cyanopyridine and isophthalonitrile.
(1) Japanese Kokai Tokkyo Koho 62-129257 discloses a method in which benzonitrile is reduced using Raney nickel or Raney cobalt in the presence of ammonia. It is, however, difficult to practice such method on the industrial basis since it requires a hydrogen pressure extremely as high as 100 kg/cm2G.
(2) U.S. Pat. No. 4,254,059 discloses a method in which benzonitrile is hydrogenated using a ruthenium-phosphine complex catalyst. Such method is again not applicable on the economical and industrial basis, since ruthenium is a kind of noble metals, phosphine as a ligand is also expensive, and 18-crown-6 used as an additive is still also expensive.
(3) Japanese Kokai Tokkyo Koho 05-097776 discloses a method in which benzonitrile and 3-cyanopyridine are hydrogenated using a cobalt-immobilized alumina catalyst and a rhodium-immobilized silica catalyst. Both of rhodium and cobalt are, however, kinds of noble metals and are less acceptable on the economical basis. Another problem resides in that the method uses a large amount of ammonia as a solvent, which inevitably promotes elution of the catalytic metals to thereby shorten the lifetime of such catalysts, and is again less acceptable on the industrial basis. While the specification exemplifies a case in which succinonitrile, one of aliphatic nitrites, is hydrogenated using a nickel-silica catalyst, the use of nickel amounts as much as 54.4 mol % of the substrate, which indicates an extremely low catalytic efficiency.
(4) U.S. Pat. No. 3,069,469 proposes a method in which isophthalonitrile is hydrogenated using a cobalt-nickel catalyst. The method, however, requires for the reaction a hydrogen pressure extremely as high as 175 to 245 kg/cm2G, which is not practical on the industrial basis.
An object of the present invention resides in that overcoming a number of the foregoing problems inherent to the prior art, and that providing a method for producing an aromatic primary amines in a high yield by hydrogenating an aromatic nitrile at a low pressure. The present inventors found after extensive studies that hydrogenation under a specific condition using a nickel-immobilized catalyst can successfully produce an aromatic primary amine at a low temperature, which led us to propose the present invention.
That is, the present invention relates to a method for producing an aromatic primary amine, characterized by hydrogenating an aromatic nitrile at a low partial pressure of hydrogen in a heterogeneous system comprising a non-reductive polar solvent and a nickel-immobilized catalyst suspended therein.
The present invention will be detailed hereinafter.
The aromatic nitrile in the context of the present invention include aromatic polynitriles having on a single aromatic ring a plurality of cyano groups, such as phthalonitrile, isophthalonitrile and terephthalonitrile. The term xe2x80x9caromaticxe2x80x9d in the present invention is used for expressing compounds having hydrocarbon-base aromatic group and heterocyclic aromatic ring, which are exemplified by those having phenyl group, naphthyl group, anthryl group, pyridyl group, furyl group or thienyl group, where all of such groups may be substituted by one or more substituents not responsible for the reaction. Examples of such substituent not responsible for the reaction include alkyl group, aromatic group, alkoxy group, phenoxy group, alkylthio group, phenylthio group, silyl group, silyloxy group, halogen atom, nitro group, amino group, amide group, hydroxyl group and composite group based on the combination of two or more thereof. For the case having two or more substituents, such substituents may differ with each other. The composite group based on the combination of two or more thereof include alkoxyalkyl group, halogenated alkyl group, silylated aromatic group, nitrophenoxy group, and N,N-dialkylamino group. While it is generally known that reactivity in the hydrogenation of aromatic nitrile largely depends on the substituents on the aromatic ring, the reaction in the present invention can proceed with a high efficiency even in the presence of such substituents.
The nickel-immobilized catalyst in the present invention refers to a catalyst which comprises a carrier and nickel immobilized thereon. The available carrier can be such that comprising a porous material, which is typified by metal oxide, composite oxide, layered clay compound and activated carbon. From the viewpoints of catalytic activity and reaction efficiency, particularly preferable examples thereof include silica, alumina, activated carbon, and arbitral combinations thereof. There is no limitation on processes for producing such immobilized catalysts, and any of those produced by known processes are available. That is, the catalyst may be produced by immersion process, ion exchange process and physical mixing process. While the amount of immobilization of catalytic metal is not specifically limited, it can generally be selected within a range from 1 to 80 wt % of the total amount of the catalyst. The amount of use of the catalyst depends on the amount of immobilization of catalytic metal and is not specifically limited, where the amount of nickel can generally be selected within a range from 0.01 to 40 mol % of aromatic nitrile as the substrate, and more preferably from 0.1 to 20 mol % from the viewpoints of reaction efficiency and economy.
The non-reductive polar solvent in the present invention refers to polar solvents not reducible by hydrogen during the reaction, and examples of which include alcoholic solvents such as methanol, ethanol, propanol, isopropyl alcohol, t-butyl alcohol, ethylene glycol, Methyl Cellosolve and phenol; ether solvents such as diethyl ether, tetrahydrofuran, dioxiane and dimethoxyethane; and water. Among which, the alcoholic solvents are preferable in terms of reaction efficiency, yield, selectivity and convenience for recovery and isolation of the product.
In the present invention, the reaction is proceeded under heated and pressurized conditions. There is no special limitation on the reaction method, and the reaction may be proceeded in a batch manner or semi-batch manner. The partial pressure of hydrogen is generally selected within a range from 0.1 to 50 kg/cm2G, where a preferable range considering safety and economy is 19 kg/cm2G or below, and more preferably 10 kg/cm2G or below. The reaction temperature can generally be selected within a range from room temperature to 200xc2x0 C., where a preferable range considering reaction efficiency, safety and economy is 80 to 150xc2x0 C.
The reaction in the present invention may be proceeded in the presence of ammonia. The presence of ammonia tends to raise the selectivity and yield. There is no special limitation on the amount of use of ammonia, it is preferably selected in general within a range from 1 to 20 mol equivalence of aromatic nitrile as the substrate, and more preferably within a range from 1 to 4 mol equivalence in terms of the reaction efficiency, yield and selectivity.
The method of the present invention will further be detailed hereinafter based on preferred Examples. It should now be noted that the present invention is by no means limited to such Examples.